Ceramic materials are typically clay-based materials which generally are very hard and manifest a high degree of resistance to corrosion and extremes of temperature and accordingly, they have been extensively used in a variety of applications. Ceramics have become an increasingly significant engineering material for systems which encounter extreme temperatures, abrasive conditions or corrosive substances. For this reason, ceramic materials are utilized for lining furnaces, chemical reactors, pipelines and the like and for fabricating turbine blades, dies and other mechanical parts.
Ceramics manifest many superior properties which make them the material of choice for particular applications; however, various other properties of these same ceramics can limit their potential uses. Ceramic materials are generally brittle and hard to cut. They cannot be easily welded or joined to provide an impervious joint and cannot be readily machined to complex shapes. Furthermore, many ceramics are highly porous. Ceramics generally have a high degree of thermal expansion; consequently rapid heating or cooling can shock the materials causing them to crack. These undesirable properties make ceramics difficult to use in many applications, as for example in the lining for pipes or furnaces or for the fabrication into complex shapes.
The term "greenware" refers to a solid, usually firable, composition of a ceramic precursor material generally fabricated at ambient, or fairly low temperatures. Greenware is converted into a ceramic material when heated to a fairly high temperature. In some instances, it is possible to cast a body of ceramic greenware into a desired shape and to subsequently fire the greenware into a ceramic body having a desired final shape. However, in many instances this approach is not feasible because many greenware compositions tend to slump, or partially melt during firing making it impossible to retain a desired shape. "Refractory", is the term applied to materials which can withstand high temperatures without adverse effect. The term is of general and imprecise use, although it is frequently applied to various high temperature resistant phosphates, silicates and the like. While refractories have good high temperature properties, many of such materials are soft, porous and/or poorly resistant to corrosive environments.
What is needed in the art is a method whereby high performance materials which exhibit the best qualities of ceramics and refractories maybe fabricated. Such materials should exhibit toughness, corrosion resistance and an impervious surface and should be fabricated without any slumping or melting during the firing process. Materials of this type could be fabricated into greenware of a desired shape and fired into articles which maintain fairly precise geometric tolerances. While there are known in the prior art, a great number of ceramic compositions and a variety of processes for the fabrication of such ceramics, none are fabricated according to the process of the present invention and none exhibit the combination of hardness, corrosion resistance and thermal resistance manifested by the materials of the present invention. Because the materials of the present invention generally embody compositions akin to refractories and because they exhibit many of the beneficial properties of ceramics, together with select properties of refractories, the materials of the present invention are referred to as "Hybrid Ceramics." These and other advantages of this invention will be readily apparent to those skilled in the art from the, discussion, description and examples which follow.